1. Field of the Invention
The present invention relates to methods of forming carbon or graphite yarn in which carbonizable precursor yarns are pre-treated as necessary and then heated in an inert atmosphere to a temperature sufficient to at least partially carbonize the yarns, with the yarns thereafter being fired, and then graphitized if desired.
2. History of the Prior Art
It is known to form carbon or graphite yarns by running carbonizable precursor yarns of materials such as continuous filament rayon through a process in which the yarns are cleaned such as by a dry cleaning process, then carbonized, then fired, and finally graphitized as desired. Cleaning removes surface finishes from the precursor yarns so that the yarns can be readily carbonized by heating to a carbonizing temperature in an inert atmosphere. The yarns are thereafter fired by heating to a temperature above about 900.degree. C. in an inert atmosphere for a relatively short period of time so as to substantially raise the percentage of carbon in the yarns. An example of such a process is provided by U.S. Pat. No. 3,294,489 of Millington et al, issued Dec. 27, 1966 and commonly assigned with the present application.
In such prior art processes the precursor yarns are typically twisted together to form a multi-ply yarn which is then processed in batches. The multi-ply yarn is wrapped on skeins and periodically severed, following which the skeins are placed in a dry cleaning tank for removal of weaving lubricants and thereafter in a carbonization oven. There are several problems with this technique including the fact that the yarn is expensive to make because of the labor involved in wrapping the skeins, severing the yarn after formation of each 1-2 lb. skein and loading the individual small skeins into batch cleaning equipment. Moreover, there is a persistent tangling problem as the yarns are wound onto and off of the skeins, resulting in substantial yield losses due to tangled yarn which cannot be used. The final yarn product itself tends to be of poor or nonuniform quality due to the limitations imposed by handling of the skeins during processing. Because the yarns must be cut after they are wrapped on the skeins, the yarn is typically cleaned, carbonized, fired and graphitized in 1-2 lb. lots. After carbonization and firing this reduces the yarn lots to on the order of 1/4-1/2 lb., requiring that the resulting yarn produced by the process have frequent knots along the length thereof as the small 1/4-1/2 lb. lots of yarn are knotted together to form the yarn.
Accordingly, it would be desirable to be able to process precursor yarns in a highly efficient and effective manner so as to produce carbon or graphite yarn having relatively low cost and with little wastage, and having generally uniform high quality. Such process should ideally lend itself to the rapid and continuous processing of the yarns in large quantities, and should permit the yarn to be processed in relatively long lengths so as to reduce the frequency of knotted joints in the resulting yarn product.
Accordingly, it is an object of the invention to provide an improved, more efficient process for forming carbon or graphite yarn from precursor yarns.
It is a further object of the invention to provide a process for making carbon or graphite yarn in which the yarns can be handled efficiently in large quantities and processed rapidly and on a generally continuous basis to produce yarn of relatively high quality and uniformity and at the same time relatively low cost.
It is a still further object of the invention to provide a process permitting yarn to be processed in substantial lengths to produce an end yarn product having relatively few knotted joints.